I've been to a few different places that host life drawing sessions, and they're all pretty similar in the basic structure of things; short poses at the start, gradually working up to longer and longer poses, then one or two much longer poses, and often shorts again to finish. I learnt pretty quickly that I much prefer shorter poses - I'm not aiming to be especially realistic (I have a camera to do that...), so I find after 15 minutes I've done all I want to do with most drawings, I much prefer the challenge of capturing a pose in few seconds or couple of minutes tops. Enough to get the shapes, and then move on. So these sort of quick drawings are often my favourites:

Alas I have longer periods to fill too. You can see with this model I really didn't get on well with her face! Indeed faces and me generally don't work out that well!